School Shows

A Star Called the Sun

Secrets of the Sun

Title graphic for the planetarium show Secrets of the Sun

Produced by Evans & Sutherland
Salt Lake City, Utah

Our Sun is a dynamic body, one star of hundreds of billions in the Milky Way. It is the most important star for our world. Until recently, many things about the Sun remained a mystery. Scientists are now using instruments to scan the Sun's surface and atmosphere and are unveiling links between solar events and the effects they have on Earth. They are probing the Sun's interior, learning how its energy is created and how long it can be sustained.

In ancient times, people believed the Sun died at sunset and was reborn at sunrise. We know the Sun has been around long enough to circle the Milky Way twenty-five times. The last time the Sun was in its present galactic position, the Earth only had dinosaurs living on the world's one continent.

The birth of the Sun took place in a cloud of interstellar dust and gas. A part of the cloud collapsed under gravitational forces until the energy reaction at its core became self-sustaining. Within a flattening disk of the remaining dust and gas, planets began to form in orbit around the stabilizing star. A final burst of energy swept lingering gas and dust away.

At the McMath Pierce solar telescope, the Sun's light is reflected down a long tunnel to an observing room, where the photosphere is seen in visible light. Beyond the photosphere is the Sun's atmosphere, the corona. Between the photosphere and corona is a thin layer called the chromosphere, where gasses fall along magnetic field lines like rain.

On a time scale measuring billions of years, the motion of stars around the Milky Way appears chaotic. Over the last few million years, continental drift has brought the lands of Earth to their present locations.

Now the Sun is observed by an array of space probes, revealing dynamic processes. The SOHO probe views the Sun in ultraviolet wavelengths, while the TRACE probe provides close-up images of the transition zone at the bottom of the Sun's atmosphere. There, the plasma has a temperature of a half million degrees Celsius.

Across the surface, there are active regions with sunspots the size of Earth and larger. The solar surface is mottled where gas is welling up from below.

The Sun behaves like a giant magnet, interacting with Earth's own magnetic field. Solar flares erupt, releasing large amounts of energy that reaches Earth. Even larger eruptions, called Coronal Mass Ejections (CMEs), race away from the Sun. When the leading edge of the CME interacts with Earth's magnetic field, electric circuits in satellites may fail, power grids on Earth may fail, and cell phones may experience outages. These same solar events also produce the glowing lights of the Northern and Southern Lights.

To see where the energy comes from, we look into the Sun. At the surface, the temperature is 6,000 degrees C, but there is no solid place to stand. As we descend, we pass through the convective layer, where 50,000 degree C gas globules the size of Texas rise then sink after they have released their energy and cooled. At 160,000 miles below the visible surface is the radiative zone, where temperatures rise to 2 million degrees. Deeper is the core, where particles fly about at 100 miles per second. Energy production at the core is the same reaction that takes place in a hydrogen bomb explosion.

Some stars live out their lives in a single rotation of the Milky Way. Our sun has been around much longer, nearly 5 billion years. In the distant future, another 5 billion years from now, the Sun will grow cooler and swallow Mercury and Venus as it swells to become a red giant star. Earth may survive, but its oceans will boil away, and life will come to an end. These changes in the Sun may make other places in the solar system suitable for life, including Jupiter's moon Europa and Saturn's moon Titan.

In its senior years, as its core swells and contracts, the Sun will shed its outer layers, forming a planetary nebula.

Related Internet Sites:
Space Weather
Mr. Eclipse